Friction-reducing devices known as bearings are available in a wide variety of types and are used in machines of virtually all sizes and complexities. A well-known type uses component parts which roll relative to other parts. For example, bicycle hubs use ball bearings, with or without a bearing "race." And every electrically powered home appliance uses one or more bearings. To enlarge the scale of the examples, railroad freight car wheels are supported on tapered roller bearings. Bearings of the foregoing types incorporate a multiplicity of rolling components such as spherical balls, solid cylindrical rollers, slender cylindrical needles or solid tapered rollers.
Such bearings share certain common features. One is that they operate at relatively high speed. Another is that they are known as "hydrodynamically" lubricated bearings in that their operating speed helps assure that critical surfaces be continually coated with a film of lubricant.
However, bearings having rolling components are by no means the only type of bearings used. Another major bearing type is a journal bearing, an example of which is a hollow-cylinder-shaped bearing. Yet another bearing type is a flat, washer-shaped thrust bearings. Journal and flat thrust bearings involve sliding rather than rolling motion. When used in high-speed applications, such bearings are hydrodynamically lubricated and in low speed applications, such bearings are known as "boundary-lubricated" bearings.
With larger machines, providing adequate bearing lubrication--especially for boundary-lubricated bearings--can present difficult problems. Nowhere is this more true than in large mobile machines such as earth-moving and earth-excavating machinery.
Such machinery is available in a wide variety of types ranging from the familiar rubber-tire mounted and crawler-track mounted to the less-common walking dragline. A dragline is often used for removing top soil and "overburden" to expose a valuable mineral, e.g., coal, beneath the earth's surface.
A dragline is equipped with an angularly-extending boom from which is suspended a "bucket" having an open mouth and digging teeth, both facing toward the main portion of the machine. Overburden is removed by placing the bucket on the ground at a point distant from the machine and pulling it toward the machine, filling the bucket in the process. Once filled, the machine pivots about a central axis and the bucket emptied at a spoil pile somewhat away from the area being excavated.
To give some perspective to the following discussion, a large walking dragline--made by Harnischfeger Industries of Milwaukee, Wis., and incorporating the invention--has a main housing portion (including the machinery deck, operator's cab and the like) which is about 105 feet long, about 80 feet wide, about 40 feet high and weighs about nine million pounds. The boom extends about 300 feet and the capacity of the digging bucket is about 80 cubic yards. The walk legs of such dragline take steps about seven feet in length.
Because a dragline bucket is often off-center of the boom and machine centerline, such bucket imposes lateral loads at the end of the boom. To accommodate such lateral loading and reduce wear on the bucket ropes, the sheave assembly at the end of the boom is capable of oscillatory motion. In a known sheave assembly, the washer-like journal bearing supporting the assembly has grease grooves located on a radius from the centerline of oscillation. Oscillation urges grease along the grooves but not across the grooves.
For a machine like the dragline described above, its mere size militates against easy maintenance. For example, lubrication of elevated parts along and at the end of the boom necessitate taking the machine out of service and moving the boom near to the ground to obtain easy access to such parts.
An improved bearing arrangement which addresses the inaccessibility of the bearing, which provides good lubrication to relatively-moving surfaces and which is suitable for use with a thrust-type journal bearing would be an important advance in the art.